Magnitude and significance of Miocene crustal extension in the central Mojave Desert, California

Abstract

The newly recognized Waterman Hills detachment fault (WHDF) of the central Mojave Desert, California, is significant because it provides the first unambiguous evidence for large-scale core complex-style crustal extension in the central Mojave Desert, and because it has significantly rearranged the pre-Miocene paleogeography of the Mojave Desert. The WHDF places steeply dipping to overturned Miocene volcanic and sedimentary rocks upon mylonitic pre-Tertiary basement. The mylonites, which apparently formed during extension, are predominantly L-tectonites which manifest top-to-northeast shear. The WHDF dips to the northeast beneath dominofaulted ranges of the central Mojave Desert and detachment faults of the Colorado River trough, forming an imbricated early Miocene system of detachment faults. Extension continued in the Colorado River trough after extension had ceased in the central Mojave Desert. Tentative correlations of Mesozoic intrusions suggest about 40 km of slip across the WHDF, which carries eugeoclinal Paleozoic rocks in its hanging wall and cratonal/miogeoclinal Paleozoic rocks in its footwall. Restoration of 40 km of slip (1) removes a prominent kink in the boundary between eugeoclinal and cratonal/miogeoclinal facies, (2) aligns cratonal/miogeoclinal strata near Victorville more closely with the late Paleozoic continental margin farther north, (3) places cratonal/miogeoclinal rocks structurally beneath eugeoclinal rocks, implying that the facies were stacked by thrusting, and (4) straightens the western margin of the Late Jurassic Independence dike swarm.